/**
 * \file MurmurHash.h
 * \brief No dependencies
 */

#ifndef __KEY_VALUE_FILE_MURMUR_HASH_H_
#define __KEY_VALUE_FILE_MURMUR_HASH_H_


namespace KeyValueFile
{
	//-----------------------------------------------------------------------------
	// MurmurHash2, by Austin Appleby

	// Note - This code makes a few assumptions about how your machine behaves -

	// 1. We can read a 4-byte value from any address without crashing
	// 2. sizeof(int) == 4

	// And it has a few limitations -

	// 1. It will not work incrementally.
	// 2. It will not produce the same results on little-endian and big-endian
	//    machines.
	inline
	unsigned int MurmurHash2( const void * key, int len, unsigned int seed )
	{
		// 'm' and 'r' are mixing constants generated offline.
		// They're not really 'magic', they just happen to work well.
		const unsigned int m = 0x5bd1e995;
		const int r = 24;

		// Initialize the hash to a 'random' value
		unsigned int h = seed ^ len;

		// Mix 4 bytes at a time into the hash
		const unsigned char * data = (const unsigned char *)key;

		while( len >= 4 )
		{
			unsigned int k = *(unsigned int *) data;

			k *= m; 
			k ^= k >> r; 
			k *= m; 
			
			h *= m; 
			h ^= k;

			data += 4;
			len -= 4;
		}
		
		// Handle the last few bytes of the input array
		switch( len )
		{
		case 3:
			h ^= data[2] << 16;
		case 2:
			h ^= data[1] << 8;
		case 1:
			h ^= data[0];
			h *= m;
		};

		// Do a few final mixes of the hash to ensure the last few
		// bytes are well-incorporated.
		h ^= h >> 13;
		h *= m;
		h ^= h >> 15;

		return h;
	}
};

#endif